Subpixel displacement and deformation gradient measurement using digital image/speckle correlation (DISC)

Experimental solid mechanics relies heavily on surface displacement and def ormation gradient measurements. Digital image/speckle correlation (DISC) us es digital image processing to resolve displacement and deformation gradien t fields. The practical implementation of DISC involves important challenge s such as computation complexity and the discrepancy of the sensitivities a nd accuracies claimed in previous studies. We develop an iterative, spatial -gradient based algorithm, which uses only first-order spatial derivatives of the images before and after deformation. Simulated images are then used to verify this algorithm, as well as to study the impact of speckle size on the accuracy. Based on these simulations, the sensitivity of DISC to displ acement and deformation gradient, as well as an optimal speckle size for op timal accuracy, is recommended. The algorithm is then calibrated using rigi d body translation and rotation, and an application of DISC to thermomechan ical diagnostics of electronic packaging is also presented. (C) 2001 Societ y of Photo-Optical Instrumentation Engineers.